A seat adjustment apparatus for a vehicle is known, at which a seat adjustment mechanism is driven with an electric motor, and thus the seat for the vehicle is adjusted. JP2010-504876T (which will be hereinafter referred to as Patent reference 1) discloses the known seat adjustment apparatus for the vehicle at which a reclining mechanism serving as the seat adjustment mechanism is driven with the electric motor, and thus a backrest angle of a seatback (the backrest) relative to a seat cushion (a seating portion) is adjusted.
According to the Patent reference 1, the reclining mechanism is arranged at each of the right side and the left side relative to the seat for the vehicle. The reclining mechanisms connect the seat cushion and the seatback to each other so that the backrest angle of the seatback relative to the seat cushion is adjustable. The reclining mechanisms, which are arranged at the right and left sides as a pair, are connected to each other by a connecting shaft (a connecting member). The reclining mechanisms are attached to end portions of the connecting shaft, respectively. The electric motor rotates the connecting shaft. Upon being rotated, the connecting shaft drives the pair of reclining mechanism so that the angle of the seatback is adjusted.
Generally, the electric motor is provided inside the seatback. The electric motor is generally arranged close to either one of the right side and left side relative to the seatback. This is because the electric motor interferes with an occupant's upper back portion and/or lower back portion in a case where the electric motor is arranged in a center of the seatback.
Recently, for a purpose of weight reduction, the connecting shaft is required to be formed thinner. In a case where the connecting shaft is formed to be thinner, a rotation angle (an angle of torsion) of an end portion of the connecting shaft, which is positioned at a side far from the electric motor, may be larger than a rotation angle of an end portion of the connecting shaft, which is positioned at a side close to the electric motor. Because a configuration of a cross section of the connecting shaft is uniform in an axial direction thereof, the rotation angle of an end portion of the connecting shaft increases in proportion to a distance to the end portion from a portion at which a rotary force is inputted. Accordingly, in a case where the reclining mechanisms arranged at the right and left sides, respectively, are actuated with the same torque, the rotation angle of the end portion that is positioned far from the electric motor is larger than the rotation angle of the end portion that is positioned close to the electric motor. In a case where the rotation angles of the respective end portions of the connecting shaft differ from each other, a difference in operation amounts is generated between the reclining mechanisms, which are provided as the pair, at the beginning of the operation of the seat adjustment apparatus for the vehicle after the start-up of the apparatus. The difference in the operation amounts leads to delay in a starting time of the operation of one of the reclining mechanisms compared to that of the other one of the reclining mechanisms. As a result, the occupant feels uncomfortable at the beginning of the operation of the seat adjustment apparatus for the vehicle after the start-up of the apparatus. This disclosure provides a seat adjustment apparatus for a vehicle, at which a difference in operation amounts between a pair of seat adjustment mechanisms is reduced.
A need thus exists for a seat adjustment apparatus for a vehicle which is not susceptible to the drawback mentioned above.